First major update of src/2_coordinates.md

src/2_coordinates.md

@@ -347,7 +347,7 @@ $$dV = r^2 \sin\theta dr d\theta d\varphi.$$
 
 We have discussed four different coordinate systems:
 
-1.  tip "*Cartesian coordinates*" 
+1.  !!! tip "Cartesian coordinates" 
     $${\bf r} = (x_1, \ldots, x_n).$$ This systems can be
     used for any dimension $n$. It is particularly convenient for: infinite spaces, systems
     with rectangular symmetry.